Conventionally, when a portion of a diagram is desired to be magnified and displayed, it has been the practice of magnifying not only the objective area (portion) but also the whole diagram as shown in diagram 101 of FIG. 1. However, with this method, the whole diagram cannot be accommodated on the display area. Another conventional practice has been to magnify the portion of the diagram desired to be magnified, and of displaying it in the vicinity of an original diagram as shown in a diagram 102 of FIG. 1. With this procedure a display area other than the area for the original diagram is needed. Therefore, in order to magnify a portion desired to be displayed in detail and display the whole diagram, portions other than the portion desired to be displayed in detail are needed to be reduced in size on the display. When the magnified portion and the reduced portions are so mixed on a display screen, it has been extremely difficult to recognize which portion is magnified or reduced, and to which extent the portion is magnified or reduced.
Therefore one object of the present invention is to provide a method and apparatus for visually displaying a diagram where a portion is magnified or reduced in a manner that the magnified/reduced area thereof and the magnification/reduction ratio can be easily determined.
Another object of the present invention is to provide a system, which is capable of displaying the magnification/reduction ratio during the magnification/ reduction operation of a diagram, to enable an easy comparison between a changed operation area and the other areas.